Blasting device



J. P. SWED BLASTING DEVICE July 3, 1956 Filed Oct. 25. 1951 K%/% A X ATTORNEii United States Patent 2,152 15 BLASTING DEVICE James PershingSwed, Gibbstowh, N. L, assignor to E. I.

du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware Application October 25, 1951, Serial No. 253,052

4 Claims. (Cl. 102 25) The present invention relates to an improved blasting tube for mining coal, and, more particularly, this invention relates to an improved assembly for holding the charge of a gas-producing material in proper position for firing, and an assemblyin which theloading of the charge into the cartridge is. facilitated.

In a co-pending application, Serial Number 174,818, filed by Davis, Glogau, Loving and Swed, a highly efiective blasting tube for mining coal is disclosed. The tube described therein is of the pressure-resistant, reusable container type, and the charge comprises ammonium nitrate packaged ina tubular container of lesser diameter than the inner diameter of the tube, so that the charge cannot pack the tube from wall towall at any point in the tube.

In order to load a tube similar to that described in the foregoing application, it is necessary to unscrew the firing head closing one end of the tube, and, in order to replace the rupture disc, it is necessary to remove the hollow threaded cap at the other end. Since both ends must be tightly closed to maintain the desired seal against pressure leakage until the rupture disc has been sheared, it is frequently difiicult to loosen these ends. In the case of the firing head, damage may be caused to the electrical elements due to wrench slippage and rough handling in the field.

It is an object of the present invention to provide an assembly whereby the necessity of removing the firing head from the tube is eliminated. A further object of the present invention is to provide an assembly whereby the charge of gas-producing material may be loaded from the discharge end and still be rigidly and properly positioned with respect to the firing head. A still further object of the present invention is to provide a charge assembly which is simple to handle and to load into the container. Additional objects will become apparent as the invention is further described.

I have found that the foregoing objects may be achieved when I provide a simple locking element at the firing head end of the pressure resistant container and utilize a relatively rigid cylindrical container for the gas-producing composition, one end of said container being closed with a plug provided with means adapted to cooperate with the said locking element to hold the charge in proper position, and to become engaged when inserted with slight force.

To more fully illustrate the present invention, two specific embodiments are shown in the accompanying drawings, the invention not being limited thereto.

In the drawings, Figure 1 is a longitudinal section of a fully assembled blasting tube utilizing the present invention; Figure 2 is a sectional view of the pressure-resistant container locking element; Figure 3 is a sectional view of the charge locking element; Figure 4 is a top view of the same element; and Figure 5 is a longitudinal section of an alternative embodiment.

Referring to the figures in greater detail, 1 represents a tubular steel cylinder having internal threads at each end. At one end of the cylinder 1 is the rupture disc 2 side source of electrical current.

2,752,849 Patented July 3, 1956 ice 21, is the electrode 12, which is insulated from the firing head 6 and the sleeve 7 by means of insulators 22, and is provided with terminal 13 for connection with an out- Terminal 14 is attached to the head 6, which is not insulated from sleeve 7, the latter providing the contact with the remaining end of the ribbon 21. The cylindrical container 15, for example, of cardboard, has one end crimped to form a closure and the remaining end closed by plug 8. Within the container 15 is the gas-producing charge 16.

The lock-on sleeve 7 contains an inwardly projecting annular ridge 17, and the prongs 9 of the plug 8 contain peripheral notches 18 adapted to be engaged by the ridge 17. The centrally-located prongs 19 serve to insure good electrical connection between the ribbon 21 and the electrode 12. To permit the slight displacement-required when the prongs 9 and 19 are entered into sleeve 7, slots.

20 are provided. These slots 20 also provide a restricted opening for the flow of gas into sleeve 7 during the pressure build-up,'so that when pressure is suddenly released by the shearing of disc 2, the plug 8 is forced out of sleeve 7.

In Figure 5, the lock-on sleeve 7 is made integral with the firing head 6.

In loading the pressure-resistant tube, the cap 3 is removed, and the charge assembly is thrust plug-end first into the opening. The contour of the tube assembly guides the charge assembly to sleeve 7, where the tapered ends of sleeve 7 guide the prongs 9 to a central position, and the force of the impact is sufiicient to push the ends of the prongs 9 inwardly so that they enter the sleeve 7. When the notches 18 are aligned with the ridge 17, the prongs snap back to the extended position and securely lock the charge assembly in place. The prongs 19 maintain one end of the heating ribbon in good electrical contact with the electrode 12, while the other end of the ribbon 21 is wedged between the sleeve 7 and one of the prongs 9. The rupture disc 2 is then inserted and the cap 3 replaced and tightened, and the blasting tube is ready for firing. Firing is accomplished by passing a current through the heating ribbon 21, which in turn heats the charge 16 until it reaches a temperature wherein it decomposes to form gaseous products. During the pressure development, the slots 20 facilitate the entrance of gas between the sleeve 7 and the plug 8. When the pressure reaches a predetermined point, the disc 2 is sheared, suddenly releasing the pressure from the cylinder. The gas behind the plug 8 forces the plug 8 out of locking engagement with sleeve 7 and towards the cap end of the cylinder, where it can easily be removed when the cap is unscrewed.

The sleeve 7 is preferably made of steel, and, as illustrated, may be made separable from the firing head 6, or may be made integral therewith. The annular ridge 17 may be replaced with a plurality of projecting beads, if desired. It is not essential that the ridge 17 have a flat edge as shown in Figure 2, and the notch 18 may be rounded if desired.

Obviously, the number of slots 20 may be varied or even eliminated, thus forming a single tubular projection or prong, depending upon the flexibility of the plug material. Similarly, the prongs in the inner ring need not be the same length as those in the outer ring.

I prefer to use a non-conducting material for the plug 8, since the necessity of insulating the heating ribbon is thereby avoided. To insure against the possibility of fiame, the plug material should have a relatively high ignition temperature. Wood and various plastics can be used, since the high temperature in the cartridge is of such short duration that ignition of the plug will not occur. Obviously, the plug material must possess sufficient resiliency so that the prongs 9 and 19 will exert a force in the direction of their normal position, yet may not be so brittle that the prongs will be broken by the impact with sleeve 7. I prefer not to use a material which is highly resilient, since such resilience introduces a rebound factor when the charge is thrust into the cylinder.

It will be noted that the diameter of the plug is substantially the same as that of the container for the charge. This greatly simplifies the packing of large numbers of charge assemblies for shipment and the handling of the assemblies in the field.

In the present illustration, the heating element has been shown as consisting entirely of a nichrome ribbon. Obviously, other electrically responsive heating means may be employed.

The invention has been described at length in the foregoing, but it will be understood that many variations in detail may be introduced without departure from the scope thereof. I intend, therefore, to be limited only by the following claims.

I claim:

1. A charge assembly for use in pressure-resistant blast- 30 ing cartridges of the type described, comprising a rigid cylindrical container, a gas-producing charge within said container, an electrically-responsive heating element in contact with said charge, and a plug of non-conducting material closing one end of said container, said plug having a plurality of prongs extending outwardly parallel to the axis thereof and forming two concentric rings, the outer ring containing a groove about the outer periphery thereof near the ends of said prongs, and an axially located aperture through said plug for the passage of a connector to said heating element.

2. A charge assembly as claimed in claim 1 wherein the plug is made of wood.

3. A charge assembly as claimed in claim 1, wherein each ring consists of at least four prongs.

4. An assembly for retaining the gas producing charge within a pressure-resistant container comprising a sleeve secured at one end of said container with its longitudinal axis in line with the longitudinal axis of the container, an inwardly projecting annular ridge at the end of the sleeve opposite said end of the container, and a plug for closing and retaining a charge of gas-producing material, said plug having a plurality of prongs extending outwardly parallel to the axis thereof and forming two concentric rings, the outer ring having a diameter substantially equal to the inside diameter of said sleeve and containing a groove about the periphery thereof near theends of the prongs, said groove being of substantially the same size and contour as said annular ridge.

References Cited in the file of this patent UNITED STATES PATENTS 707,626 Norres Aug. 26, 1902 2,207,191 Geertz July 9, 1940 2,253,549 Barton Aug. 26, 1941 

1. A CHARGE ASSEMBLY FOR USE IN PRESSURE-RESISTANT BLASTING CARTRIDGES OF THE TYPE DESCRIBED, COMPRISING A RIGID CYLINDRICAL CONTAINER, A GAS-PRODUCING CHARGE WITHIN SAID CONTAINER, AN ELECTRICALLY-RESPONSIVE HEATING ELEMENT IN CONTACT WITH SAID CHARGE, AND A PLUG OF NON-CONDUCTING MATERIAL CLOSING ONE END OF SAID CONTAINER, SAID PLUG HAVING A PLURALITY OF PRONGS EXTENDING OUTWARDLY PARALLEL TO THE AXIS THEREOF AND FORMING TWO CONCENTRIC RINGS, THE OUTER RING CONTAINING A GROOVE ABOUT THE OUTER PERIPHERY THEREOF NEAR THE ENDS OF SAID PRONGS, AND AN AXIALLY LOCATED APERTURE THROUGH SAID PLUG FOR THE PASSAGE OF A CONNECTOR TO SAID HEATING ELEMENT. 